The motion converting device of this invention was conceived and developed as a part of a transducer for use in vehicle power steering systems of the type using an electrical servo motor. In such systems, it is desired to develop an electrical signal which represents the magnitude and direction of the torque applied by the driver to the steering wheel of the vehicle. Such a signal is useful for controlling the energization of the servo motor for turning the dirigible wheels of the vehicle.
It is desirable in a power steering system of the type described, to have an angular displacement transducer which can produce the desired electrical signal in response to relative angular displacement between the steering wheel shaft and the input shaft of the steering gear with a torsionally resilient element between the two shafts to establish a relationship between torque and relative angular displacement. As used herein, an angular displacement transducer is a device that may produce an electrical signal corresponding to the angular displacement and/or to any time derivative of the angular displacement, such as angular velocity, angular acceleration, etc.
An angular displacement transducer for use in vehicle power steering systems must be capable of generating the desired signal even though the relative angular displacement is small. Further, it must be of compact and rugged construction and must lend itself to ease and economy of manufacture. Further, it should be adapted for installation between a driving and driven shaft, preferably in a coaxial relationship therewith.
The requirements for such angular displacement are admirably satisfied by use of a motion converter in which relative angular displacement is converted into linear displacement, preferably with amplification, in conjunction with a linear displacement sensor.
The prior art includes devices for torque measurement which are of general interest. The Templin U.S. Pat. No. 4,135,390 discloses an arrangement in which an engine shaft is bolted to the hub of a flex plate which has its outer periphery fastened to a torque converter of a transmission. An arcuate array of slots extending between the hub and the periphery of the drive plate define a plurality of spokes which carry the torque. The spokes bend or flex by an amount proportional to the torque and electromagnetic pickups are employed to obtain a measure of the spoke deflection. The Ruge U.S. Pat. No. 2,403,952 describes a torquemeter comprising a pulley with flexible spokes. Strain gages are placed on the spokes to produce an electrical signal corresponding to torque.
As will be become evident from the description that follows, this invention is addressed to the problem of converting relative angular displacement into linear displacement. As used herein, the term linear displacement means motion of a body which is substantially the same as or approximates rectilinear translation, as that term is used in the field of analytical mechanics. As discussed above, such a motion converter is useful in an angular displacement transducer. It will be recognized that such a converter is also useful in many other applications including for example, measurement and control devices as well as transducers of various kinds which involve input and output motion.
A general object of this invention is to provide an improved device for converting relative angular displacement to linear displacement.